The present invention relates to a novel norbornene derivative, a fluorine-containing polymer prepared by copolymerizing the norbornene derivative, and a chemically amplifying type photoresist composition which is excellent in transparency and possesses improved dry etching resistance.
As a result of an increasing necessity for high integration of a large scale integrated circuit (LSI), microfabrication technology is required for photolithography. In order to satisfy such requirements, there have been tried to use, as exposure light sources, a deep ultraviolet, a KrF excimer laser (wavelength: 248 nm) and a ArF excimer laser (wavelength: 193 nm) which have a wavelength shorter than conventional g-rays (wavelength: 436 nm) and i-rays (wavelength: 365 nm). Those light sources are put into practical use.
Recently a process using a F2 laser (wavelength: 157 nm) having a wavelength in a vacuum ultraviolet region has been studied in an ultra-microfabrication technology and is considered promising as an exposure technology aiming at a technology node of 0.1 μm.
On the other hand, in the pattern formation, a chemically amplifying type resist which becomes advantageous in transparency, resolution, sensitivity and dry etching resistivity in cases of energy rays having various wavelengths has been studied. The chemically amplifying type resist means, for example, in case of a positive resist, an energy-sensitive composition comprising a resin soluble in an alkali developing solution and having an introduced substituent which has an effect of inhibiting dissolution of the resin but is deprotected due to action of an acid, and a compound which generates an acid by irradiation of energy rays such as light and electron beam (hereinafter referred to as a photoacid generator). When the composition is irradiated with light or electron beam, an acid is generated from the photoacid generator, and by heating (post-exposure bake, hereinafter referred to as “PEB”) after the exposure of light, the substituent which has been giving a dissolution inhibiting effect on the resin is deprotected due to action of an acid. As a result, the exposed portion becomes soluble in alkali, and by treating the exposed portion with an alkali developing solution, a positive resist pattern can be obtained. In that case, the acid acts as a catalyst and exhibits its effect in a very small amount. Also action of the acid becomes active by the PEB and a chemical reaction is accelerated like a chain reaction, and thus sensitivity is enhanced.
Examples of conventional resins for chemically amplifying resist are phenol resins in which a part or the whole of hydroxyl is protected by a protective group such as acetal or ketal (KrF resist), methacrylic acid resins in which an acid-labile ester group is introduced to carboxyl (ArF resist) and the like.
However those conventional resist polymers have strong absorption in a wavelength range of vacuum ultraviolet region and have a significant problem that transparency against F2 laser having a wavelength of 157 nm which is studied in a process for ultra fine pattern is low (a molecular absorption coefficient is high). Therefore in order to expose with F2 laser, it is necessary to make a resist film thickness very thin and it is substantially difficult to use the polymers as a single layer F2 resist.
R. R. Kunz, T. M. Bloomstein, et al. suggest in Journal of Photopolymer Science and Technology (Vol. 12, No. 4 (1999) 561–569) that fluorocarbons have good transparency at 157 nm as compared with various materials and have possibility of use as a F2 resist.
However in that literature, there is only description that existing fluorocarbon polymers are high in transparency at 157 nm, but there is no description as to preferable structure of fluorine-containing polymers. Also with respect to a fluorine-containing polymer having functional group necessary, for example, for a positive type or negative type chemically amplifying resist, not only evaluation of transparency but also synthesis of the polymer is not made. Moreover the literature does not suggest a fluorine-containing base polymer material being preferable as a chemically amplifying resist and a preferable resist composition obtained therefrom at all, and there is found no possibility of forming a F2 resist pattern by using a fluorine-containing polymer.
Thereafter A. E. Feiring, et al. of E. I. du Pont de Nemours and Company disclosed in PCT Patent Publication WO00/17712 (published Mar. 30, 2000) that a specific fluorine-containing polymer is useful for F2 resist application.
That patent publication describes the use of a fluorine-containing polymer having a structural unit of fluoroolefin and a structural unit having a polycyclic structure.
Further an acid-labile (acid-decomposable) functional group necessary for a positive type resist is introduced to a fluorine-containing polymer by copolymerizing a conventional acrylic, methacrylic, norbornene or vinyl ester monomer with a monomer having an acid-labile (acid-decomposable) functional group. However there is no example of a polymer having a structural unit in which an acid-labile group which is changed to —C(Rf)(Rf′)OH is directly bonded to a norbornene backbone.
Also a norbornene derivative is disclosed as one example of a polycyclic structure constituting a fluorine-containing polymer for a resist and a halogen-substituted norbornene is described, but there is no description as to an example of a fluorine-substituted norbornene, a norbornene simultaneously substituted by fluorine atom and an acid-reactive group in one molecule or a norbornene having a fluorine atom or acid-reactive group at specific position.
Further thereafter A. E. Feiring, et al. of E. I. du Pont de Nemours and Company disclosed in PCT Patent Publication WO00/67072 (published Nov. 9, 2000) that a fluorine-containing polymer having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb is useful for F2 resist application.
In that patent publication, a structural unit of norbornene in which —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb is bonded through a part of —CH2OCH2—. However there is no description as to an example of —C(Rf)(Rf′)OH being directly bonded to a norbornene backbone.
Further there is disclosed norbornene derivatives having —C(Rf)(Rf)OH or —C(Rf)(Rf′)O—Rb as an example of a fluorine-containing polymer to be used for a resist. Among them, there is disclosed a halogen-substituted norbornene. However there is concretely no description as to an example of a fluorine-substituted norbornene, a norbornene simultaneously subjected to substitution of fluorine atom and the above-mentioned acid-reactive group in one molecule or a norbornene subjected to substitution at a specific position.
Further Katsuyama, et al. of Matsushita Electric Industrial Co., Ltd. proposed a method of forming a pattern with exposure light having a wavelength of from 1 to 180 nm using a resist material containing halogen atom (JP2000-321774A published Nov. 24, 2000). However there is disclosed only a methacrylic resin having a structural unit of methacrylic ester having —CH2CF3 group and —CH(CF3)2 group in its side chain as a base resin having halogen atom for a resist, and no resin containing fluorine atom in its trunk chain is disclosed. Also there is concretely disclosed no polymer which has a structural unit of fluorine-containing monomer having functional group and fluorine atom simultaneously and can act as a chemically amplifying resist (positive type or negative type). Further there is no description as to a polymer having a cyclic structure in its trunk chain.
Also there is generally known that dry etching resistivity of a polymer is enhanced by introducing a norbornene backbone to the polymer. However transparency, particularly transparency in a vacuum ultraviolet region of conventional norbornene derivatives cannot be said to be sufficient. In the present invention, it was found that transparency, particularly transparency in a vacuum ultraviolet region is enhanced by introducing fluorine atom or a fluorine-containing group to a specific position of a norbornene derivative.
Also in conventional resist polymers though an acid-reactive group necessary for a resist polymer is introduced by polymerizing an ethylenic monomer (acrylic monomer, etc.), transparency (particularly transparency in a vacuum ultraviolet region) and dry etching resistivity are lowered by the introduction. In the present invention it was found that when an acid-reactive group necessary for a resist together with fluorine atom or fluoroalkyl group are introduced to one molecule of a norbornene derivative simultaneously, both of good transparency (particularly transparency in a vacuum ultraviolet region) and dry etching resistivity can be imparted to a fluorine-containing polymer obtained by polymerizing the norbornene derivative.
The first object of the present invention is to provide a novel fluorine-containing norbornene derivative and a process for preparation thereof.
The second object of the present invention is to provide a novel fluorine-containing polymer obtained by copolymerizing the novel fluorine-containing norbornene derivative.
The third object of the present invention is to provide a chemically amplifying photoresist composition which comprises a fluorine-containing polymer having a fluorine-containing norbornene unit and acid-labile group, and a photoacid generator, and can be used for a patterning process using F2 laser as light source.